Fact · Speech recognition
The jiwer README says that applying an empty reference and hypothesis pair to the WER formula is undefined behaviour, because it divides by zero.
Checked against its source on October 17, 2026
In the source's own words
“There is undefined behaviour when you apply an empty reference and hypothesis pair to the WER formula, as you get a division by zero.”
jiwer: Evaluate your speech-to-text system (README), Jitsi open source project, GitHub, jitsi/jiwer, n.d., Section: A note on empty references.
Open the original- What it measures
- The jiwer README explains how its package treats empty references. The formula divides errors by the number of reference words, so an empty reference leaves the denominator at zero.
- What it does not show
- The passage describes one package's handling of an edge case. It does not say how other scoring tools treat empty references.